Re: [PATCH v4 7/7] kernel.h: drop trace_printk.h

[Joel Fernandes <joelagnelf@nvidia.com>]

On Mon, Dec 29, 2025 at 11:17:48AM -0500, Steven Rostedt wrote:
> On Sun, 28 Dec 2025 13:31:50 -0800
> Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > > trace_printk() should be as available to the kernel as printk() is.  
> > 
> > um, why?  trace_printk is used 1% as often as is printk.  Seems
> > reasonable to include a header file to access such a rarely-used(!) and
> > specialized thing?
> 
> It will waste a lot of kernel developers time. Go to conferences and talk
> with developers. trace_printk() is now one of the most common ways to debug
> your code. Having to add "#include <linux/trace_printk.h>" in every file
> that you use trace_printk() (and after your build fails because you forgot
> to include that file **WILL** slow down kernel debugging for hundreds of
> developers! It *is* used more than printk() for debugging today. Because
> it's fast and can be used in any context (NMI, interrupt handlers, etc).
> 
> But sure, if you want to save the few minutes that is added to "make
> allyesconfig" by sacrificing minutes of kernel developer's time. Go ahead
> and make this change.
> 
> I don't know how much you debug and develop today, but lots of people I
> talk to at conferences thank me for trace_printk() because it makes
> debugging their code so much easier.
> 
> The "shotgun" approach is very common. That is, you add:
> 
> 	trace_printk("%s:%d\n", __func__, __LINE__);
> 
> all over your code to find out where things are going wrong. With the
> persistent ring buffer, you can even extract that information after a
> crash and reboot.

I use trace_printk() all the time for kernel, particularly RCU development.
One of the key usecases I have is dumping traces on panic (with panic on warn
and stop tracing on warn enabled). This is extremely useful since I can add
custom tracing and dump traces when rare conditions occur. I fixed several
bugs with this technique.

I also recommend keeping it convenient to use.

thanks,

 - Joel